As the chemicals in the baths of a photographic processor are used up, replenishment chemicals must be added to the baths in order to keep the activities and concentrations of the chemicals constant.
The amount of replenishment is dependent on many factors, e.g., light exposure given to the photographic material, the properties of the photographic material and the ability of the replenisher to restore a process tank solution to its aim concentration.
The replenishment of a process is often carried out automatically. This may be accomplished by using an algorithm or look-up table for calculating the amount of replenishment required. The algorithm may be dependent on area alone as practised in most automatic processing machines; or it may be dependent on exposure as described in EP-A-0,596,994; U.S. Pat. No. 5,235,369; EP-A-0,500,278; EP-A-0,456,684 and U.S. Pat. No. 4,486,082; or the algorithm may be dependent on the amount of silver developed in a black and white system as taught by EP-A-0,596,991, U.S. Pat. Nos. 5,315,337, 5,073,464, GB-A-2,108,707 and GB-A-2,106,666.